1. Field of the Invention
This invention relates to apparatus for interfacing field wiring with the input/output circuits of an electrical control or monitoring system. More particularly, it relates to a modular system in which the number of types of signal processing modules required for a particular input/output application are reduced by employing a personality module having a selection of configurations for interfacing the signal processing modules with the field wiring.
2. Background Information
Electronic control systems and monitoring systems such as process control systems require communication with the real world. This includes receiving inputs such as commands and process conditions provided by various sensors, transducers and/or contacts, and generating outputs such as control signals, status and results. This interaction is provided by input/output (I/O) hardware. The signals passed through the I/O can be analog and/or digital. Typically, the I/O includes signal processing circuitry which for example can limit the range of analog signals, provide filtering, amplification or attenuation, surge protection, isolation, pulse shaping for digital signals, and other signal conditioning. Different types of interfaces can be required for connecting the signal processing circuitry to various external devices connected to the I/O through field wiring. For instance, some current sensors require an external source of power. In some applications, a sensing resistor is required to convert a current signal to a voltage signal. In some applications, the field wiring requires local grounding while in other cases field grounding is provided.
Conventionally, this interfacing is provided as part of the I/O circuitry, typically on a plug-in I/O card. Although the signal conditioning applied may be identical for various types of field signals, separate I/O cards providing the different interfaces required must be used and inventoried.
Modular I/O units are being offered in which a selection of I/O cards each packaged in an electronic module can be plugged into a base which includes a backplane providing connections between circuits in the electronic module and terminals to which the field wiring is connected. The base units are mounted side-by-side on a standard DIN rail and plugged into one another for communication with a controller over a common bus system. A system of this type is shown in U.S. Pat. No. 5,472,347. While such an arrangement makes it easier to provide the necessary range of interfacing with the field wiring, it still requires the use and inventorying of many different types of electronic modules.
There is a need, therefore, for an improved I/O for connection with field wiring.
More particularly, there is a need for improved I/O for interfacing with field wiring which minimizes the number of configurations of signal processing cards required.
There is an additional need for such an I/O system which is modular for ease in adapting the system to a particular application.